1. Field of the Invention
The present invention relates to drive axle assemblies for motor vehicles and methods for assembling the same in general, and more particularly to a method for verifying predetermined bearing preload of a differential assembly module during the operation of mounting the differential assembly module to a support beam member of the drive axle assembly.
2. Description of the Prior Art
Drive axle assemblies are in common use in most motor vehicles. Such axle assemblies include a number of components that are adapted to transmit rotational power from an engine of the motor vehicle to wheels thereof. Typically, the drive axle assembly includes a hollow axle housing, a differential assembly, which is rotatably supported within the axle housing by a non-rotating differential carrier. The differential assembly drivingly couples an input drive shaft extending from the vehicle engine and a pair of output axle shafts extending to the vehicle wheels. Typically, the axle shafts are contained in respective non-rotating tubes of the axle housing. Thus, rotation of a gear mechanism of the differential assembly by the drive shaft causes corresponding rotation of the axle shafts.
Typically, a differential case of the differential assembly is rotatably supported by the differential carrier through a pair of single row tapered roller bearings adapted to accurately center the differential case within the differential carrier and accurately position a ring gear relative to a drive pinion. Proper engagement of the ring gear carried by the differential case with the driving pinion is necessary for proper operation. The differential case must rotate with considerable precision, lest the ring gear will not mesh properly with a drive pinion gear of a final drive assembly and thereby produce noise and excessive wear. To achieve this precision, the differential case and the differential carrier must not only be machined accurately, but the bearings must be set properly to a condition of an appropriate, predetermined preload where no radial or axial end play exists in the differential case. The preload in the bearings imparts rigidity to the differential case, but too much preload will cause the bearings to overheat and fail prematurely. On the other hand, too little preload may cause the bearings to acquire the end play, and this likewise decreases the life of the bearings and introduces radial and axial play into the differential case.
Generally, the prior art differential case bearings have been made adjustable by means of adjustment shims or threaded sleeve adjusters used to provide the predetermined preload on the differential case bearings according to manufacturer's specification.
Typically, the differential case bearings are disposed within the differential carrier and preloaded to the predetermined preload prior to mounting the differential case within the differential carrier. The accuracy of the differential bearing preload depends largely on a workmen's experience. After that, the assembled differential carrier is fastened to an axle housing of the drive axle.
Unfortunately, common assembly problems do affect differential bearing preload, such as: (1) improper fitting or misalignment of either the outer bearing race rings into the differential carrier bore or the inner bearing race rings onto the differential case, (2) presence of foreign particles in or about the race rings, and (3) workmen's skill in wrongly controlling compression to obtain the predetermined preload as a result of torquing the threaded sleeve adjusters. If such problems are not detected prior to putting the differential assembly into service, it will have a useful life significantly shortened, and often irreparable damage could be done requiring replacement of bearings or other components.
However, if the differential bearing assemblies are not properly preloaded, then it is practically impossible to verify the accuracy of the bearing preloading during the process of assembling the drive axle. When it is realized during the testing or operation of the drive axle that the differential bearings are not properly preloaded, the axle has to be disassembled, the differential carrier dismantled from the axle housing and the preload of the differential bearings has to be adjusted. It may require several disassembling-reassembling operations before the correct bearing preload is achieved. Such labor-intensive procedures add cost and complexity to the drive axle manufacturing procedure.
Thus, there is a need for a method for verifying a predetermined bearing preload of the differential assembly during the process of assembling of the drive axle that enables plant personnel to quickly determine differential bearing preload conditions to see if they all fall within specific design parameters, thus preventing premature axle failure and enhancing reliability of the differential assembly.